This is a multi-centre, randomised, placebo-controlled, double-blind parallel group study in adult subjects with Crohn's disease who previously achieved clinical response (CDAI decrease of at least 100 points) and/or remission (CDAI less than 150) in a prior Phase III induction study (Study CCX114151 or another GSK sponsored induction study). Subjects will be randomised to 52 weeks of oral treatment with GSK1605786A 500 mg once daily or 500 mg twice daily or placebo. Subjects who are receiving concomitant corticosteroids at entry will undergo dose tapering following a defined schedule. Subjects who complete the treatment period may be eligible to enter an open-label extension study. Subjects who experience disease worsening and require additional (rescue) treatment will be withdrawn and may be eligible to enter the open-label study. Subjects who do not enter the open-label study must complete a follow-up assessment 4 weeks after completion of treatment. Approximately 756 subjects will be enrolled.